1. Field of the Invention
The present invention relates to a toner and a developer.
2. Description of the Related Art
In recent years, demand has arisen on the market for toners having various advantageous properties such as small particle diameters for forming high-quality output images, high temperature offset resistance, low temperature fixing ability for energy saving, and heat resistant storage stability during storage after production or during conveyance of a product at high temperature and high humidity. Particularly, power consumption for fixation accounts for a large proportion of the power consumed in an image forming step, and improvement of the low temperature fixing ability is extremely important.
Conventionally, toners produced by kneading-pulverizing method have been used. Toners obtained by the conventional kneading-pulverizing method are not easily made to have a small particle diameter, and each have an indeterminate shape, and broad particle size distribution. Thus, output images have insufficient quality. Furthermore, these toners have various problems such as requiring a large amount of energy for being fixed. In particular, when toner materials including wax (releasing agent) for improving fixing ability are used to produce a toner by the kneading-pulverizing method, cracks occur at the interfaces of the wax during pulverization, resulting in that the wax exists on the toner surface in a large amount. As a result, although the releasing effects can be obtained, toner adhesion to a carrier, a photoconductor and a blade is likely to occur. The properties of such toners are not satisfactory in total.
In order to overcome the above-described problems the kneading-pulverizing method has, there is proposed a method for producing a toner by a polymerization method. According to the polymerization method, toners are made easily to have a small particle diameter. Their particle size distribution is sharper than that of the toners obtained by the pulverizing method. Furthermore, the wax can be embedded in the toner particles. As one exemplary method for producing a toner by the polymerization method, Japanese Patent Application Laid-Open (JP-A) No. 11-133665 discloses a method for producing a toner using, as a binder, an elongated product of a urethane-modified polyester for the purposes of improving the low temperature fixing ability and hot offset resistance of the toner.
Also, JP-A Nos. 2002-287400 and 2002-351143 disclose a method for producing a toner having excellent fluidity and transferability as powder with a small particle diameter as well as being excellent in heat resistant storage stability, low temperature fixing ability and high temperature offset resistance.
Japanese Patent (JP-B) No. 2579150 and JP-A No. 2001-158819 disclose a method for producing a toner including an aging step for producing a toner binder having a more stable molecular weight distribution and for attaining both low temperature fixing ability and high temperature offset resistance.
However, these proposed techniques do not satisfy high level of low temperature fixing ability demanded recently.
In order to obtain high level of low temperature fixing ability, there is a proposal of a toner containing a crystalline polyester resin-containing resin and a releasing agent, wherein the resin and the wax are incompatible with each other, to thereby form a sea-island phase separation structure (for example, Japanese Patent Application Laid-Open (JP-A) No. 2004-46095).
Moreover, there is a proposal of a toner containing a crystalline polyester resin, a releasing agent and a graft polymer (for example, JP-A No. 2007-271789).
However, by the techniques of these proposals, heat resistant storage stability, high temperature offset resistance, and high-level low temperature fixing ability can be obtained, but the crystalline polyester resin and the releasing agent are not sufficiently dispersed, causing filming.
Therefore, currently there is a demand for a toner having excellent low temperature fixing ability, high temperature offset resistance, and heat resistant storage stability without causing filming, and a developer containing the toner.